In my U.S. Pat. No. 3,485,521 there is illustrated a seal of the padlock type, in which the body is formed of a synthetic organic plastic with a pair of apertures opening to one end of the body, and the shackle is formed of a U-shaped piece of wire having reverse bent end portions, which end portions, when inserted into the body openings, are locked therein by the end portion being maintained in a flexed condition so that the end of the reverse bent portion digs into the wall of the housing aperture.
Although the seal as illustrated in the above-identified patent has achieved considerable commercial success, it has been found that in some instances it has been possible to work an end of the shackle out of its aperture to enable the seal to be removed and re-assembled without leaving evidence of tampering.
It has been proposed that if the end portions of the shackle were bent outwardly, rather than inwardly, as illustrated in said patent, such attempts to remove a shackle end would cause the extreme end to pierce the outside wall of the housing. However, in such case, the protruding reversely bent end can be cut off, and the remainder of the leg pulled out of the housing. When, after the protected closure has been opened, the seal can be re-assembled by forming a new reverse-bent end portion on the end of the leg that has been cut off.
Such seals must often be removed by authorized service personnel, which can be done only by cutting the spring steel shackle with a special type of wire cutter. Such tools are expensive and often lost by the service personnel.